Nanotubes grow up

Aug 14, 1998

Chinese researchers have created the world's largest ever carbon
nanotube. They created the 2mm long nanotube using a new technique in which
acetylene is passed over a catalyst in a nitrogen atmosphere (Nature394 631).

The technique uses an iron-silica catalyst created by coating a quartz plate with an
iron-silica solution. Once the solution dries it cracks into a film 30-50 microns thick.
After the substrate is heated in a vacuum and then in a hydrogen-nitrogen atmosphere
to make sure that it becomes chemically unreactive,
the film breaks into large
quantities of iron-silica nanoparticles. The researchers noticed that the nanotubes
became longer if the acetylene was passed over the catalyst for a long period. By
increasing the length of time still further,
they hope to exceed their new record.
Nearly all the nanotubes produced by this method grow in parallel arrays from the
catalyst surface,
making them easy to remove.

Meanwhile,
a team of French and Chinese scientists has constructed nanotubes that
can act as'coaxial cables' (Science281 973). Zhang and his colleagues achieved their
breakthrough with nanotubes 50 micrometers long and a few tens of nanometers in
diameter. They managed to form a nanotube with three 'jackets' each with different
conducting properties. Such behaviour will make nanotubes prime candidates for the
developing nanoelectronic components. They found that if they used a selection of
boron nitride,
carbon,
silicon oxide and lithium nitride compounds,
the nanotubes
form inside each other in a series of 3 layers. A core layer of silicon carbide
(semiconducting); an intermediate layer of amorphous silicon oxide (insulating); and a
shell of boron nitride and carbon (semiconducting). The authors speculate that by
adjusting the quantities of the starting compounds,
it may be possible to build self-
organising nanocables with different components inside them.